Psoriasis is characterized by increased epidermal proliferation and immune activation. Successful therapy must normalize one or both of these features. Psoriatics benefit from phototherapy after exposure to UV irradiation alone or in combination with photosensitizing systemic or topical drugs. Tin protoporphyrin (SnPP) and tin-mesoporphyrin (SnMP) are synthetic, photosensitizing heme analogues. In this open pilot study we are testing our hypothesis that photochemotherapy with SnPP and SnMP may be generally useful for psoriatics and may prove to have a therapeutic advantage over PUVA therapy.